gpar {grid} | R Documentation

## Function to produce a Graphical Parameter Object

### Description

This function returns an object of class `"gpar"`. This is basically a list of name-value pairs.

### Usage

    gpar(...)

### Arguments

`...` | Any number of named arguments.

### Details

All grid viewports and (predefined) graphical objects have a slot called `gp`, which contains a `"gpar"` object. When a viewport is pushed onto the viewport stack and when a graphical object is drawn, the settings in the `"gpar"` object are enforced. In this way, the graphical output is modified by the `gp` settings until the graphical object has finished drawing, or until the viewport is popped off the viewport stack, or until some other viewport or graphical object is pushed or begins drawing.

Valid parameter names are:

col | Colour for lines and borders.
fill | Colour for filling rectangles, polygons, ...
lty | Line type
lwd | Line width
fontsize | The size of text (in points)
fontfamily | The font family
fontface | The font face (bold, italic, ...)
lineheight | The height of a line as a multiple of fontsize
font | Font face (alias for fontface; for backward compatibility)

For most devices, the `fontfamily` is specified when the device is first opened and may not be changed thereafter – i.e., specifying a different font family via `fontfamily` will be ignored. This will hopefully change in future versions of R. Also, there is an important exception: `fontfamily` may be used to specify one of the Hershey Font families (e.g., `HersheySerif`) and this specification will be honoured on all devices.

The specification of `fontface` follows the R base graphics standard: 1 = plain, 2 = bold, 3 = italic, 4 = bold italic.

Specifying the value `NULL` for a parameter is the same as not specifying any value for that parameter, except for `col` and `fill`, where `NULL` indicates not to draw a border or not to fill an area (respectively).

All parameter values can be vectors of multiple values. (This will not always make sense – for example, viewports will only take notice of the first parameter value.)

### Value

An object of class `"gpar"`.

### Author(s)

Paul Murrell

### See Also

`Hershey`.

### Examples

    gpar(col = "red")
    gpar(col = "blue", lty = "solid", lwd = 3, fontsize = 16)
    grid.newpage()
    vp <- viewport(w = .8, h = .8, gp = gpar(col="blue"))
    grid.collection(grid.rect(gp = gpar(col="red"), draw = FALSE),
                    grid.text(paste("The rect is its own colour (red)",
                                    "but this text is the colour",
                                    "set by the collection (green)", sep = "\n"),
                              draw = FALSE),
                    gp = gpar(col="green"), vp = vp)
    grid.text("This text is the colour set by the viewport (blue)",
              y = 1, just = c("center", "bottom"),
              gp = gpar(fontsize=20), vp = vp)
    grid.newpage()
    ## example with multiple values for a parameter
    push.viewport(viewport())
    grid.points(1:10/11, 1:10/11, gp = gpar(col=1:10))
    pop.viewport()

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